Super-junction schottky diode

ABSTRACT

The present invention relates to the field of semiconductor technology, particularly to a super-junction schottky diode. According to the present invention, the effective area of schottky junction is increased by forming the schottky junction in the trench located in the body of the device. Therefore, the current capacity of this novel schottky diode can be greatly improved. In addition, a super-junction structure is used to improve the device&#39;s reverse breakdown voltage and reduce the reverse leakage current. The super-junction schottky diode provided in the present invention can achieve a larger forward current, a lower on-resistance and a better reverse breakdown characteristic.

CROSS REFERENCE

The present application is based on, and claims priority from, Chineseapplication number 201610596069.4, filed on Jul. 25, 2016, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of semiconductordevices, particularly to a super-junction schottky diode.

BACKGROUND OF THE INVENTION

Diodes are one of the most commonly used electronic devices. The typesof traditional diodes are schottky diodes and PN junction diodes. PNjunction diodes can withstand high reverse blocking voltage and hasbetter stability. However, PN junction diodes have a larger forwardvoltage and a longer reverse recovery time. Schottky diodes are based onthe principle of metal-semiconductor junction. Schottky diodes have alower forward voltage and a faster reverse recovery since it has nominority carrier accumulation during the forward conduction. However,schottky diodes have a larger reverse leakage current and a poortemperature characteristic. There is a tradeoff between schottky diode'sbreakdown voltage and the forward voltage, which is called the “siliconlimit”. In order to improve the breakdown voltage of a schottky diode,the thickness of drift region must be enhanced and the dopingconcentration of drift region must be reduced, which leads to anincrease of forward conduction loss. Therefore, the main applicationfield of schottky diode is for low or middle voltage applications.

In order to improve the schottky diode's breakdown voltage withoutincreasing its forward voltage, the super-junction structure isintroduced into the schottky diode's drift region. For example, Chinesepatent application “A super-junction schottky semiconductor device andits preparation method” (application number: 201210141949.4) provided aschottky diode based on the charge balance principle. However, theschottky junctions existing in schottky diodes are located on thesurface of the devices, so that the current capacity of the schottkydiode is limited since the surface area is limited.

SUMMARY OF THE INVENTION

The present invention provides a novel super-junction schottky diode.The effective area of the schottky junction is increased by forming theschottky junction at the trench located in the body of the device.Therefore, the current capacity of the novel schottky diode can begreatly improved. In addition, a super-junction structure is used toimprove the device's reverse breakdown voltage and reduce the device'sreverse leakage current.

According to an aspect of the invention, there is provided asuper-junction schottky diode including: a metallized cathode electrode1, a N+ substrate 2 (i.e., a heavily doped substrate of a conductivitytype N), an N-type drift region 3 (i.e., a drift region of aconductivity type N), and a metalized anode electrode 9. Said N-typedrift region 3 includes a P-type buried layer 4 (i.e., a buried layer ofa conductivity type P), a P-type column 5 (i.e., a column of aconductivity type P), a P+ heavily doped region 6 (i.e., a heavily dopedregion of a conductivity type P), a N-type lightly doped region 8 (i.e.,a lightly doped region of conductivity type N), and a trench 7. TheP-type buried layer 4 is under the trench 7, and the top surface of theP-type buried layer 4 contacts with the bottom surface of the trench 7.The P-type column 5 is located between two adjacent trenches 7. The P+heavily doped region 6 is disposed above the P-type column 5, and thebottom surface of the P+ heavily doped region 6 contacts the top surfaceof the P-type column 5. The N-type lightly doped region 8 is located onthe side of the trench 7 and on the top surface of the N-type driftregion 3. Said trench 7 is filled with metal, and the metal togetherwith the N-type lightly doped region 8 form a schottky junction. The topsurface of the N-type lightly doped region 8 is covered with metal thatis the same as the metal in the trench 7, and the metal together withthe N-type lightly doped region 8 also form a schottky junction. The topsurfaces of said metal and the P+ heavily doped region 6 contact thebottom surface of the metalized anode electrode 9. The junction depth ofsaid P-type buried layer 4 is the same as the that of the P-type column5.

Additionally, the bottom surface of said P-type buried layer 4 andP-type column 5 can contact the top surface of the N+ substrate 2.

Furthermore, the P-type buried layer 4 can be replaced with the thickoxide layer 10.

Some beneficial effects of the present invention are as follow. Comparedto the existing super-junction schottky diode, the structure of thisinvention has a larger forward current, a smaller forward voltage, and abetter reverse breakdown characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic sectional view of a power device accordingto the Embodiment 1 of the present invention.

FIG. 2 shows a diagrammatic sectional view of a power device accordingto the Embodiment 2 of the present invention.

FIG. 3 shows a diagrammatic sectional view of a power device according,to the Embodiment 3 of the present invention.

FIG. 4 to FIG. 12 show diagrammatic sectional views of steps forfabricating the device in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, the features of the variousexemplary embodiments may be understood in combination with thedrawings.

Embodiment 1

As shown in FIG. 1, the first embodiment of the present inventionprovides a super-junction schottky diode.

FIG.1 illustrates a super-junction schottky diode in accordance withthee present invention. The super-junction schottky diode includes: ametallized cathode electrode 1, a N+ substrate 2, an N-type drift region3 and a metalized anode electrode 9. Said N-type drift region 3 includesa P-type buried layer 4, a P-type column 5, a P+ heavily doped region 6,an N-type lightly doped region 8 and a trench 7. The P-type buried layer4 is under the trench 7, and the top surface of the P-type buried layer4 contacts with the bottom surface of the trench 7. The P-type column 5is located between two adjacent trenches 7. The P+ heavily doped region6 is disposed above the P-type column 5 and the bottom surface of theheavily doped region 6 contacts the top surface of the P-type column 5.The N-type lightly doped region 8 is located on the side of the trench 7and on the top surface of the N-type drift region 3. Said trench 7 isfilled with metal, and the metal together with the N-type lightly dopedregion 8 form a schottky junction. The top surface of the N-type lightlydoped region 8 is covered with metal that is the same as the metal inthe trench 7 and the metal together with the N-type lightly doped region8 also form a schottky junction. The top surfaces of said metal and theP+ heavily doped region 6 contact the bottom surface of the metalizedanode electrode 9. The junction depth of said P-type buried layer 4 isthe same as the that of the P-type column 5.

The mechanism of the present super-junction schottky diode provided byembodiment 1 will be explained as follows.

During the forward conduction period, the metalized anode electrode 9 isapplied with high potential and the metallized cathode electrode 1 isconnected to a low potential (e.g., ground). The trench 7 is filled withmetal, and the metal trench together with the N-type lightly dopedregion 8 form a schottky junction. Because the trench 7 is embedded inthe body of the device, the trench's sidewall area is large and thus theeffective area of the schottky junction is enlarged. Therefore, thecurrent capability of this power diode can be improved. In addition, theforward conduct voltage drop can be decreased to reduce the forwardconduction loss by increasing the doping concentration of the N-typedrift region 3 since there is a super-junction structure in the N-typedrift region 3. The doping concentrations of the N-type lightly dopedregion 8 and the N-type drift region 3 can be designed independently. Asa result, a lower turn-on voltage can be obtained by decreasing thedoping concentration of the N-type lightly doped region 8, and a lowerforward conduction voltage can be achieved by increasing the dopingconcentration of the N-type drift region 3.

During the reverse blocking period, the metalized anode electrode 9 isconnected to a low potential and the metallized cathode electrode 1 isat a high potential. The P-type column 5 together with the N-type driftregion 3 with a relatively high doping concentration can realize acharge compensation and generate a horizontal electric field. Thishorizontal electric field depletes the N-type drift region 3 and thenthe electrical characteristic of the N-type drift region 3 is the sameas the one of the intrinsic semiconductors in the vertical direction.Therefore, this schottky diode can withstand higher reverse breakdownvoltage, and the reverse leakage current is decreased. Additionally, thehorizontal electric field will appear between the P-type buried layer 4and the N-type drift region 3. Therefore, the reverse breakdown voltageis increased and the reverse leakage current can be further reduced.What's more, since the P-type buried layer 4 is located at the bottom ofthe metal trench 7, the reverse leakage current can be reduced.

In embodiment 1, the structure of the present invention can be producedby the following steps.

Step 1—monocrystalline silicon preparation and epitaxy: The N-type driftregion 3 with a certain thickness and doping concentration is depositedon the N-type heavily doped monocrystalline silicon substrate 2 by vaporphase epitaxy (VPE) or other methods, as shown in FIG. 4.

Step 2—etching trench: A hard mask 11 (such as silicon nitride) isdeposited on the surface of the silicon wafer as a barrier layer forsubsequent etching. Then the hard mask 11 is etched after thelithography and then the deep trench is etched by the shelter of hardmask 11, as shown in FIG. 5. The etching process can be reactive ionetching or plasma etching.

Step 3—P-type column epitaxy: The deep trench is filled with P-typesilicon material by an epitaxy process. Subsequently, superfluous P-typesilicon on the surface of the wafer is removed by chemico-mechanicalpolishing (CMP). Thus, the P-type column 5 is formed, as shown in FIG.6.

Step 4—etching trench again: Another hard mask 12 (such as siliconnitride) is deposited on the surface of the silicon wafer as a barrierlayer for subsequent etching. Then the hard mask 12 is etched after thelithography and then the deep trench is etched by the shelter of hardmask 12, as shown in FIG. 7. The etching process can be reactive ionetching or plasma etching.

Step 5—implanting ion: As shown in FIG. 8, P-type buried layer 4 isformed on the bottom of the trench by ion implantation with the shelterof hard mask 12.

Step 6—implanting ion again: As shown in FIG. 9, the hard mask 12 isremoved before the ion implantation. A bevel ion implantation is adaptedto implant P-type impurity ions. The N-type lightly doped region 8 isformed by impurity compensation of the implanted P-type impurities withthe N-type drift region 3.

Step 7—filling metal: As shown in FIG. 10, the deep trench is filledwith proper schottky metal (such as Platinum). The metal together withthe N-type lightly doped region 8 form schottky junction.

Step 8—etching contact hole: As shown in FIG. 11, the metal above theP-type column 5 is etched to produce a contact hole. The P-type heavilydoped region 6 is formed by P-type ion implantation.

Step 9—depositing metalized electrode: As shown in FIG. 12, metal isdeposited. on the top surface of the device to form the anode, electrode9. The anode electrode 9 is contacted with the metal trench 7 and theP-type heavily doped region 6. Then the back of wafer is thinned and thecathode electrode 1 is produced by metallization.

Embodiment 2

As shown in FIG. 2, based on the embodiment 1, the P-type column 5 andthe trench 7 are extended. The bottom surfaces of both P-type column 5and trench 7 touch the substrate 2. The beneficial effect of thisembodiment is that the reverse breakdown voltage and leakage current ofthe device can be improved further.

Embodiment 3

As shown in FIG. 3, based on the embodiment 1, the P-type buried layer 4is replaced with the thick oxide layer 10. The breakdown can heprevented to occur at the bottom of the trench 7 and thus the reversebreakdown voltage of the device can be unproved.

In addition, other semiconductor materials such as silicon carbide,gallium arsenide, indium phosphide and germanium silicon can be used toreplace silicon in manufacturing.

What is claimed is:
 1. A super-junction schottky diode, comprising:metalized cathode electrode; a N+ substrate; an N-type drift region; anda metalized anode electrode, wherein said N-type drift region includes aP-type buried layer a P-type column, a P+ heavily doped region an N-typelightly doped region, and a trench, the P-type buried layer is below thetrench, and as top surface of the P-type buried layer contacts with abottom surface of the trench, the P-type column is located between twoadjacent trenches, the P+ heavily doped region is located above theP-type column, and a bottom surface of the P+ heavily doped regioncontacts with a top surface of the P-type column, the N-type lightlydoped region is located on a side of the trench and in a top surface ofthe N-type drift region, said trench is filled with metal, and the metaltogether with the N-type lightly doped region form a schottky junction,a top surface of the N-type lightly doped region is covered with themetal, and the metal together with the N-type lightly doped region forma schottky junction, a top surface of said metal contacts with a bottomsurface of the metalized anode electrode, and the P+ heavily dopedregion contacts the bottom surface of the metalized anode electrode, anda junction depth of said P-type buried layer is the same as the that ofthe P-type column.
 2. The super-junction schottky diode according toclaim 1, wherein the bottom surface of said P-type buried layer and thebottom surface of the P-type column 5 contact with a top surface of theN+ substrate.
 3. The super-junction schottky diode according to claim 1,wherein said P-type buried layer below the trench can be replaced with athick oxide layer.
 4. The super-junction schottky diode according toclaim 2, wherein said P-type buried layer below the trench can bereplaced with a thick oxide layer.